Method and apparatus for reproduction of angular magnetic recording



Jan. 4, 1949. D. E. suNsTEm METHOD AND APPARATUS FOR REPRODUCTION OFANGULAR MAGNETIC RECORDING Filed May 3, 1945 7 emceo f mouu'ron /6 Q 1 7/8 9 /0 22 cmmsn VOLTAGE BALANCED ,L0w-

AODER J FILTER IMODULATOR 2 "FILTER OUTPUT BALANCED 8 I9 I 3/ e I 5MODULATOR ,2 a/'\ k/e (Z0 Z3\ ll) ouunoa r28 40 6 f 1 2 /Z7 62 33CARRlER VOLTAGE LOW-PASS AUDIO I :fi fiO$C1LLATOR ADDERJFILTER ma FILTERW MODLLATOR 30 6/ 33 /f 15 7 f z/ P w I L I i g 43 I FIG.3

IN V EN TOR.

DAVID E. SUNSTEIN mwzi ATTORNEYS Patented Jan. '4, 1949 OFFICEV METHODAND APPARATUS FOR REPRODUC- TION OF ANG'ULAR MAGNETIC RECORD- ING DavidE. Sunstein, Elkins Park, Psi, assignor to Philco Corporation, a c

vania orporation of Pennsyl- Application May 3, 1945, Serial No. 591,675

18 Claims. (01.179-1002) My invention relates to systems for recordingMore the magnetic flux at right angles to the axis of the wire is causedto vary along the wire in accordance with the tones of the sound beingrecorded. In this transverse method of recording the magnetic flux goesfrom one side of the wire through the wire to the other side, and thuson one side of the wire there will be a north pole 2 in it, and the onewhich previously had zero flux through it would have maximum fluxthrough it, and consequently, maximum induced voltage. At first thought,it might appear that a simple addition of the voltages from these twocoils would provide a solution to the problem. This, however, is not so,since there is a special position of the wire in which the voltages inthe two coils oppose each other, and, thus, it they were added together,the result would be zero. Consequently, using a pair of pick-up coils,the system for combining the voltages induced into two pick-up coilsmust be more complicated than the simple addition process. 7

Furthermore, it must have the characteristics that as the two are addedtogether, the relative at one particular spot and on the opposite sideof the wire there will be a south pole. Halfway around the wire therewill be neither a north pole nor a south pole, so no magnetic flux willemanate from the wire at thispoint.

If now, as the wire runs through the repro ducing mechanism, the wireshould twist on its axis, so that the reproducing pick-up coil should bepointed at the spot-on the wire, half way between the north and thesouth .pole, there wouldbe no magnetic .fiux entering'the pick-up coil,even though magnetic flux were present in the wire. This magnetic fluxwould then be at right angles to the pick-up coil, but no signal wouldbe received. This is one of the major difilculties with the system ofrecording sound on round wire by the transverse method.

It is the purpose of my invention to provide a means for picking up thesound recorded on the wire independently of the twisting of the wire. Indoing this I use two pick-up coils oriented at right angles to oneanother. In general, under these circumstances, each of the coils willpick up a signal from the wire, since the wire would be oriented withthe maximum magnetic flux part way in between the two pick-up coils.Under two special circumstances, however, one of the coils would nothave any voltage induced in it, that is, one coil would have maximumvoltage induced in it and the other coil would have zero voltage inducedin it, since this second coil would be opposite the point on the wirewhere there was no magnetic flux and from which there was no magneticflux emanating. If the wire were twisted from this position by 90degrees the roles of the two coils would be interchanged, that is theone which previously had maximum flux in it would now have zero flux upcoils are displaced with respect to one anmagnitude of the voltages intotwo coils is un-. important. Anotherwayfof saying thisis that as thetwo-arejaddedtogether the angle at which 1 themagnetic'; axis'pf thewire irests with respect H to theaxis-of either oneiof the coils mustbeanimportant, as fares the; output of the final sys-.

tem is concerned.-

It is this type, of ,asystemgwhich is the subject of the presentapplication" and generally set forth as follows: In' order to accomplishthis purpose, I transmit the signals from the two coils into twomodulators, thus, superimposing" other by mechanical degrees). Bydephasing the carriers I can add the output signals on the twomodulators in a voltage adder, and I find that the output of thisvotlage adder has the essential characteristics which I am looking for,namely, the angular position of the wire on which the recording is madedoes not enter into the amplitude of the output of the voltage adder.

This output signal from the voltage adder is, nevertheless, still asignal which has been superimposed on a carrier. The problem, then, isto demodulate this'signal so that only the audio frequency will bepresent.

One of the several methods of doing this is to pass the output of thevoltage adder through a band .pass filter which removes one of the sideband signals present in the output of the voltage adder, and then topass this output through a detector which may also be supplied with thesame carrier signal as was supplied to the modulators associated withthe pick-up coils.

The output of this detector, then, will contain a series of frequencies.One band ofthese frequencies will be the audio band which is desired,and this audio band can be separated by means of a low pass filter onthe output of the detector.

The output of this low pass filter, then, is the standard audio outputwhich is desired.

When this system is described as I have done above, it seems that thereare a considerable number of components to it. However, it is perfectlypossible in designing such a system to incorporate in one unit severalof the functions which I have described above.

Thus, for example, the low pass filter which separates the audio signalfrom-the rest oi the signals afterthe last detection or modulation canvery readily be built in to the detector, or, if it is desired toamplify the output, it can readily be built into the characteristics ofthis amplifier, so that the amplifier itself would be an amplifier whichwill-pass only audio frequencies and will not pass the supersonicfrequencies. such as those which might be used for thecarrier in thissystem.

Likewise, thevoltage adder which has been mentioned above may veryconveniently be merely a center ta ped resistor. or may merely requirethe parallel or series connection of two signals, so that when thesystem is laid out in terms of individual components. that is tubes,resistors, capacitors, coils, etc.. it is not unduly complicated.However. when the system is subjected to analysis, it will be found thatin one way or another each one of the processes mentioned above has beencarried out therein.

The fundamental purpose of my invention 4 applicable to a recording of aplurality of frequencies. This single frequency wave I shall representas A cos MT.

i i Thus the signals induced in these two coils are given by thefollowing two Equations 1 and 2:

(1) eii=A sin 0 cos Mt (2) e a==A cos 0 cos Mt .twist of the wire. Thisisbrought into the then is to provide a means for picking up the signalsfrom a wire carrying transverse sound recording and to pick this signalup in such a way that it can be reproduced electronically independentlyof the twisting of the wire in the original recording.

Still another purpose of my invention is to provide a method forreproducing the signal transversely recorded on magnetic round wire insuch a way that twistin of the wire does not introduce a difficulty.These urposes and other pur-' poses of mv invent on will become moreapparent after a-studv of t e details of the invention. This is bestcarried out by reference to the figures in wh ch:

Figure 1 shows a block diagram of one method 4 of accom lishing myinvention.

method of accomplishing my invention, and

Figure 3-shows a detailed schematic diagram of one met od of accom lshing m invention.

I now will make reference to Fi ure 1. and shall give an analysis of theperformance of this system.- The wire 1 u on which the sound is recordedis shown in cross section. An arrow 33 is drawn through this wire toshow the direction in which the magnetic flux is existing at thisparticular instant. The angle 0 is observed to be the angle between thisflux 33 and the axis of one 01' the pickup coils 3. The other pick-upcoil 2 is oriented at right angles to pick-up coil 3.

As the wire is fed through this pick-up system, it travelsperpendicularly to the plane of the paper in this drawing. As it moves,variations in voltage are induced in coils 2 and 3 in accordance withthe signal recorded on the wire. For the purposes of the analysis ofthis systemI shall consider that the recording consists of a singlefrequency within the audio range but it is equation by the factor sin 0.

Likewise, the voltage on line I! is given by Equation 2, and here againthe angle 0 enters in. but this time it comes in as the cosine function,i. e., cos 0. I

The two signals .are fed into the two balanced modulators and 5. Thesebalanced modulators are also fed with carrier signals from carrieroscillator 6. These two signals of carrier freon line H: r (3) cia=B sinct k (4) ei4=B cos ct The theory of the balanced modulator indicatesthat the output voltage 'ofthe modulator will be substantially theproduct of the two input voltages except for frequency components whichareentirely outside the range here considered.

Thus, the output of balanced modulator l is given on line l5, and thisvotlage is as given in Equation 5:

(5) el5==AB sin 0 cosMt sin ct Likewise, the output on line It is givenby Equation 6 as the product of Equation 2 and Equation 4:

(6) eie=AB cos 0 cos Mt cos ct It will be noted that each of thesecontains the product of: the amplitudes of the carrier and the pick-upsignals, a function of the angle of the wire, the audio frequency beingpicked up and the carrier frequency.

When Equations 5 and 6 are added together there is obtained the outputof the voltage adder I:

(7) (em=AB cos Mt (sin 6 sin ct+cos 9 cos ct) in which the term AB cosMt has been factored out from the sum. By means of the well knowntrigonometric equivalents this equation can be rewritten in the form ofEquation 8:

(8) (eia=AB cos Mt cos'(ct-9 means for reducing this signal to an audiotone.

'In order to analayze the operation of the reof Equation 9:

in which the standard trigonometric formula for the product of thecosines has been used. This splitting up of the Equation 8 shows thatthe signal on the output of the voltage adder can also be considered tobe the sum of signals of two different frequencies, one of which is thecarrier minus the audio frequency and the other of which is the carrierplus the audio frequency.

A filter 8 is used to eliminate one of these side band frequencies. Thisfilter may pass either the lower or upper sideband, but in the followinganalysis, the filter is chosenv as a low pass filter which eliminatesthe band above the carrier frequency. Thus, the'output On line ft ismerely the first term in Equation 9 which is given in Equation 10:

(10) cos [(c-M)t] this balanced bodulator 9 will be satisfactory.

Thus, the output of balanced modulator 9 is substantially the product ofthe signal on line I 9 and a signal on line 20 (which is the same as thesignal on line l4). The output of balanced modulator 9 is given byEquation 11, the product of Equations 4 and 10:

(11) e =g cos ct cos [(c-M)t--0] Again employing the formula for theproduct of two cosines, this Equation 11 can be changed to Equation 12:12 (22;? cos Mwm g cos [(2c M)t0] Inspection of this equation shows thatthere is one term which contains the audio frequency only, and anotherterm which contains a frequency of twice the carrier frequency minus theaudio frequency. If the carrier frequency is sufficiently high, thissecond term can be removed by low pass filter I0, so that the output online 22 is only the first term of Equation 12, as given in Equation 13:

It is to be observed that this equation contains the angle of theorientation of the wire as a phase angle in the audio frequency.Reasonable amounts of distortion in the angle of the wire will be of noimportance in disturbing the output signal.

Another method for carrying out a similar procedure is shown in Figure2. Here the modulators are not balanced, so the outputs of thesemodulators 23 and 24 contain in addition to sde hand signals, thecarrier wave. This permits line 20 of Figure 1 to be omitted in Figure2. The outputs of the modulators are fed through lines 23 and 29 into avoltage adder 23. This is fed over line 30 into a filter 40, whichremoves one side band. The output of this filter is fed, over line CI todetector 23 which may be a square law detector. The operation of thissystem gives asthe output of the detector the audio frequency componentsimilar to that shown in Equation 13, along with carrierfrequencycomponents and frequencies in that vicinity. These high frequencies arefiltered out by low pass filter 21 and the audio output appears on line32.

Still another arrangement and combination of this system is shown inFigure- 3. Here the blocks are broken down to show possibleconfigurations of the components within the blocks. This diagram ispatterned after the block diagram of Figure l with modifications. Thepickup coils 2 and 3 are shown in Figure 1. Each of the balancedmodulators 4 and 5 contain a pair of diodes and load resistors andcondensers. The

balance modulators shown in Figure 3 are balanced for the modulatingsignal, whereas the ones described in connection with Figure 1 arebalanced for carrier signals. The voltage adder 1 consists of a pair ofresistors. The filter 8 is a standard low pass filter and. theoscillator 5 is a standard tickler coil feed back oscillator.

In place of balanced modulator 9, however, I have inserted into thisdiagram a plate detection device 33. In this device the carrier signalis fed over line 20 to the cathode of the tube and the combined signaldefined in Equation 10 is fed over line i9. This is equivalent tosupplying the grid circuit of the tube with a signal such as Equation10, plus Equation 4 which is the carrier signal by itself. Since thisdetector works on a square law, it becomes necessary to determine thesquare of the input to this detector. This input is given by Equation14:

' AB (14) e cos [(cM)t-0]+D cos ct where D cos ct is the effectivecarrier signal supplied to the detector 33; that is, the vectorialdifference in carrier level on lines 19 and 20.

It is seen that when this is squared, the squares of the individualterms will yield frequencies which are all above the carrier frequencyrange,

that is the frequencies which will be provided by these squared termswill be twice the frequencies of the terms themselves, and in additionthere will be a steady D, C. component which will be unimportant.

However, the cross product of the two terms which is given by the squarelaw detector also shown in Equation 13 which is the desired signal andis the same signal that came out of the circult of Figure 1.

In this particular schematic diagram of Figure 3, a simple capacitor 43is shown as an audio low pass filter after the detector, in addition tothe coupling circuit indicated. This simple low pass circuit is adequatesince the audio amplifier and sound reproducing systems will not respondto frequencies above the audio range anyway.

The above analysis was carried out considering only a single wave forthe audio frequency. If, however, in Equations 1 and 2 we introduce cosMit plus cos Mat, we find that in the output of the balanced modulators5 and 6 there is ob- I auas s -termwithMreplacedbyM:. Suchapairoi termswould follow on through the analysis until Equation 13 Breached,though'there would-be no cross modulation between variousaudio-irequencies.

Thus, it becomes evident that a p p s or my invention is to providemeans for obtaining the output from a magnetized wire without amplitudevariations being caused by the angle of twist oi the wire. This I haveaccomplished in the systems which I have disclosed here by the processof taking output from two coils placed at right angles and by properlycombining these with a carrier, adding them, and then by properlyreditiveterms similarto ducing these modulated carrier signals to audiosignals again. Since there are several combinations of circuits whichwill accomplish this basic idea, I prefer not to have my inventiondescribed and limited by the above description, but to have it describedby the following claims. 3

I claim: a

1. In a magnetic wire reproducing which transverse'recordings are umagnetic wire, a plurality of pick-up coils angularly disposed aboutsaid wire, output circuits for each of said coils and meansfor producingsignals modulated in accordance with the signal output oi. said pick-upcoils and means for adding said modulated signals. a

2-. In a magnetic wire reproducing system in which transverse recordingsare utilized on the magnetic wire, a plurality of pick-up coilsangularly disposed about. said wire, output circuits for each of saidcoils, a first and second carrier frequency means for modulatingeach-carrier individually by one of said signal output circuits fromsaid pick-up coils and means for adding said modulated signals.

3. In a magnetic wire reproducing system in which'transverse recordingsare utilized on the magnetic wire, a plurality. of pick-up coilsangularly disposed about said wire, output circuits for each of saidcoils, a first and second carrier wave of the same frequency, means.formodulating eachcarrier individually by an associated one or systemsaid signal output circuits from said pick-up coils,

and means for adding said modulated signals.

4. In a magnetic wire recording. system in which transverse, recordingsare utilized on the magnetic wire, a pair of pick-up coils displacedfrom each other about said wire by 90 mechanical degrees; outputcircuits for each of said coils, a first and second carrier wave of thesame frequency but displaced one from the other by 90 electricaldegrees, means for modulating each carrier individually by an associatedone of said signal output circuits from said pick-up coils and means foradding said modulated signals.

5. In a magnetic wire recording system in which transverse recordingsare utilized on the magnetic wire, a pair of pick-up coils displacedfrom each other about said wire by 90 mechanical onthe 8 whichtransverse recordings are utilized onthe magnetic wire, a pair 0!pick-up coils displaced from each other about said wire by 90 mechanicaldegrees; output eircuits for 'each of said coils, a

first andsecond carrier wave of the same frequency but displaced onefrom the other by 90 electrical degrees, means for modulating eachcarrier individually by the output of an associated one oi said pick-upcoils, means (or adding said modulated signals, and means fordemodulating the resultant, so that only the audio frequency recorded onthe wire remains, comprising-a band pass filter and a detector connectedin the output of said adder means. 1

7. Ina magnetic wire reproducing system in which transverse recordingsare utilized on the magnetic wire, a plurality of pick-up coilsangularly disposed about said wire, output circuits for each of saidcoils, a balanced modulator con nected in each of said output circuitsand an oscillator for feeding said modulators.

8. In a magnetic wire recording system in which transverse recordingsare utilized on the magnetic wire, a pair or pick-up coils displacedfrom each other about said wire by 90 mechanical degrees: outputcircuits for each of said coils, a balanced modulator connected in eachor said output circuits and an oscillator for feeding said modulators,the signal currents to said modudegrees; output circuits for each ofsaid coils, a I

first and second carrier wave of the same frequency but displaced onefrom the other by 90 electrical degrees, means for modulating eachcarrier individually by an associated one of said outputs from saidpick-up coils, means for adding said modulated signals, and means fordemodulating the resultant, so that only the audio frequency recorded onthe wire remains.

lators irom said oscillator being displaced 90 electrical degrees fromeach other.,-

9. In a magnetic wire recordingsystem' which transverse recordings:- aremade; onthe magnetic wire, a pair of pick-upcoils displaced from eachother about said-iwire by-90'mechanical degrees; output cir "for each o1' said coils, a balancedmodula nneoted-in eaoh'oiisaidi cll ot 'f usf imodulators, the-signal; to said ,modula tors from said-oscillatorbeingdisplaced QOf'eleQ? trical degrees from each other and a voltageadder connected infthe 'out-pu circuits;v of; saidbalanced modulators? 110. In a magnetic wire} recording system inwhich transverse recordingsare made on the magnetic wire, a pair or pick-up coils displaced: fromeach other about saidwire by 90 mechani cal degrees; output-circuits foreach 01 said coils; a balanced modulator connected in each olsaidfoutput circuits and an oscillator for feeding saidmodulators, the signalcurrents to said modulators from said oscillator beingdisplaced 90 elecjtrical degrees from each other, and ,a'voltage adder connected in theoutput circuits 'oisaid balanced modulators, and a demodulator connectedin the output of said voltage adder.

1 1. In a magnetic wire recording system in which transverse recordingsare utilized on the magnetic wire, a pair of pick-up coils displacedfrom ach other about said wire by 90 mechanical degrees; output circuitsfor each of said coils, a balanced modulator connected in each of saidoutput circuits and an oscillator for feeding said modulators,- thesignal currents to said modulators from said oscillator being displaced90 electrical degrees from each other, a voltage adder connected in theoutput circuits of said'balanced 6. In a ma netic wire recording systemin cordance with the recording and as a function of the angle oftransverse recording axis and thereafter electrically eliminating fromthe reproduced signal those signals which are a function of thetransverse angle of recording.

13. In a magnetic wire reproducing system in which transverse recordingsare utilized on a magnetic wire, magnetic reproducing means for pickingup signals varying in accordance with the recording and varying inaccordance with the angle of the transverse recording with respect tothe reproducing means and electronic means for producing from saidpicked up signals, signals varying only in accordance with therecording.

14. In a magnetic wire reproducing system in which transverse recordingsare made on magnetic wire, a plurality of pick-up coils angularlydisposed about said wire, each of said coils having an output circuitand each of said coils being energized by the component of the signalrecording on the wire determined by the angular position of the axis ofthe coil with respect to the direction of the flux of the recording, asource of oscillations for each of said coils, the oscillations for oneof said coils being phase displaced with respect to the oscillations forthe other of said coils in amounts depending on the physical angulardisplacement of said coils with respect to each other, and meansincluding the output circuits of each of said coils for modulating saidoscillations in accordance with the signals flowing in the outputcircuits of said coils.

15. In a magnetic wire reproducingv system in which transverserecordings are made on magnetic wire, a plurality of pick-up coilsangularly disposed about said wire, each of said coils having an outputcircuit and each of said coils being energized by the component of thesignal recording on the wire determined by the angular position of theaxis of the coil with respect to the direction of the flux oi therecording, a source of oscillations for each of said coils, theoscillations for one of said coils being phase displaced with respect tothe oscillations for the other of said coils in amounts depending on thephysical angular displacement of said coils with respect to each otherand being 90 displaced from each other when the axes of said coils are90 physically displaced, and means including the output circuits of eachof said coils for modulating said oscillations in accordance with thesignals flowing in the output circuits of said coils.

16. In a magnetic wire reproducing system in which transverse recordingsare made on magnetic wire, a plurality of pick-up coils angularlydisposed about said wire, each of said coils having an output circuitand each of said coils being energized by the component of the signalrecording on the wire determined by the angular position of the axis ofthe coil with respect to the direction of the flux of the recording, asource of oscillations for each of said coils, the oscillations for oneof said coils being phase displaced with respect to the oscillations forthe other of said coils in amounts depending on the physical angulardisplacement of said coils with respect to each other, means includingthe output circuits of each of said coils for modulating saidoscillations in accordance with the signals flowing in the outputcircuits of said coils, and means for combining said modulated signalsand producing a resultant audio signal in accordance with the recordingsand independent of the flux angle of said recordings with respect to theaxis of any reproducing coil.

17. In a magnetic wire reproducing system in which transverse recordingsare made on magnetic wire, a plurality of pick-up coils angularlydisposed apart about said wire, each of said coils being energized bythe component of the signal recording on the wire determined by theangular position of the axis of the coil with respect to the directionof the flux of the recording, a source of oscillations, and meansincluding said output signals of said coils for modulating saidoscillations, the oscillations for the output of one of said coilsbeing'90 phase displaced from the oscillations for the other of saidcoil outputs in amounts depending on the physical angular displacementof said coils with respect to each other. 18. In a magnetic wirereproducing system in which transverse recordings are made on magneticwire, a plurality of pick-up coils angularly disposed about said wire,each of said coils having an output circuit and each of said coils beingenergized by the component of the signal re cording on the wiredetermined by the angular position of the axis of the coil withrespectto the direction of the fiux of the recording, a source of oscillationsfor each of said coils, the oscillations for one of said coils beingphase displaced with respect to the oscillations for the other of saidcoils in amounts depending on the physical angular displacement of saidcoils with respect to each other, means including the output circuits ofeach of said coils for modulating said oscillations in accordance withthe signals flowing in the output circuits of said coils, a voltageadder, and means for applying the modulated signals produced by theoutput of each of said coils, and means for demodulating the resultantsignal in the output of said voltage adder. @31 DAVID E. SUNSTEIN.

REFERENCES CITED The following referencesare of record in the -flle ofthis patent:

UNITED STATES PATENTS Number Name I Date 1,707,260 Fetter Apr. 2. 19291,828,189 Kilian! Oct. 20, 1931 2,245,286 Marzocchi June 10, 1941FOREIGN PATENTS Number Country Date 593,565 Germany Feb. 28, 1934

